When taking a photograph, it is sometimes desirable to have a shallow depth of field (DOF). This allows one to achieve artistic effects, in which a portion of the scene is in focus and the remainder of the scene is out of focus. For example, one may use a shallow DOF so that a flower in a scene appears in sharp focus and the more distant background appears out of focus. This prevents the flower from being lost against the background.
Depth of field depends on a number of factors, including the aperture size of the camera. The larger the aperture, the shallower is the DOF.
Shallow DOF (large aperture) may be achieved with professional SLR cameras. Unfortunately, less expensive cameras (such as cell phone cameras and small point and shoot cameras) typically have small lens apertures that cannot achieve such shallow DOF, and thus cannot create the same artistic defocus effects that may be achieved with a professional SLR camera.